Not applicable.
1. Field of the Invention
The present invention relates generally to disk drives, and in particular to a method of balancing a disk pack using a spindle motor imbalance and a disk drive including a balanced disk pack.
2. Description of the Prior Art
The typical hard disk drive includes a disk drive base, and a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to the disk drive base. The head disk assembly includes at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA) that includes at least one transducer head, typically several, for reading and writing data from and to the disk. The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
The spindle motor typically includes a spindle motor base, a central shaft, a rotatable spindle motor hub, a stator, a magnet attached to the hub, and vertically spaced upper and lower ball bearing sets mounted upon the central shaft which facilitate rotational attachment of the hub to the spindle motor base. Each ball bearing set includes inner and outer ball bearing races which encase a plurality of ball bearings. The inner ball bearing races engage the central shaft and the outer ball bearing races engage the hub. This configuration allows for rotational movement of the outer ball bearing races relative to the inner ball bearing races for rotation of the hub. The hub further includes an outer flange which is used to support one or more of the disks. The upper and lower ball bearing sets are preloaded in compression to maintain the hub and the disks supported on the hub in an orthogonal configuration with respect to the central shaft. The stator includes a series of coils and is concentrically positioned about the central shaft, adjacent the hub. With this general configuration, the various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet otherwise associated with the hub, thereby imparting a rotational motion onto the hub. Rotation of the hub results in the rotation of the attached disks.
The various rotating elements associated with the disks may be referred to as a disk pack. This may include not only the disks, but also the rotating portions of the spindle motor, the spacers, the disk clamp and disk clamp screws. It is crucial that the mass of the disk pack is balanced so as to minimize dynamic vibrations during operation of the disk drive. The greater the magnitude of the imbalance is contemplated to degrade the disk drive performance not only in terms of read/write errors, but also seek times. A significant amount of imbalance may even result in damage or excessive wear to various disk drive components.
There have been various prior art attempts to balance the disk pack. For example, one method is described in U.S. Pat. No. 5,824,898 (incorporated herein by reference). According to this method, the disk drive is assembled with the disks being attached to the spindle motor with a disk clamp. However, the disk clamp screws are only slightly torqued so as to loosely couple the disks to the spindle motor. The spindle motor is then activated to rotate and a sensor is used to detect an imbalance location of the disk pack. The disk pack is then impacted by a solenoid hammer based upon the detected imbalance location. This process may be repeated as necessary. As a result the disks may be shifted in location so as to reduce the amount of imbalance. Such a method, however, requires that the spindle motor be spun up to speed and undergo the use of the solenoid hammer as many times as required. Such a balancing process can take a significant amount of time thereby impacting the overall fabrication time of the disk drive. In this regard, there is a need in the art for an improved method of balancing a disk pack of a disk drive in comparison to the prior art.
An aspect of the present invention can be regarded as a method of balancing a disk pack for use in a disk drive. The disk pack includes a spindle motor and a rotatable disk. The spindle motor is configured to rotate the disk about an axis of rotation of the spindle motor. The spindle motor has a spindle motor imbalance location indicia upon the spindle motor indicative of a location of a spindle motor location imbalance. The method includes detecting the spindle motor imbalance location indicia. The method further includes placing the disk upon the spindle motor. The method further includes attaching the disk to the spindle motor with the disk being off-set from the axis of rotation based upon the detected spindle motor imbalance location indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation.
According to various embodiments, an optical sensor may be used to detect the spindle motor imbalance location indicia. The spindle motor may have a spindle motor imbalance magnitude indicia upon the spindle motor indicative of a magnitude of a spindle motor location imbalance. The method may further include detecting the spindle motor imbalance magnitude indicia and attaching the disk to the spindle motor with the disk off-set from the axis of rotation based upon the detected spindle motor imbalance magnitude indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation. An optical sensor may be used to detect the spindle motor imbalance magnitude indicia. The disk drive may include a disk drive base and the spindle motor may include a spindle motor hub. The method may further include attaching the spindle motor to the disk drive base and rotating the spindle motor hub in relation to the detected spindle motor imbalance location indicia and the disk drive base. In addition, the method may further include placing multiple disks upon the spindle motor and attaching the disks to the spindle motor with the disks off-set from the axis of rotation based upon the detected spindle motor imbalance location indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation. A disk clamp may be used to attach the disk to the spindle motor.
The off-set may be maximized. For example, the spindle motor may include a spindle motor hub and the disk may include an inner edge. The method may include biasing a portion of the inner edge of the disk against a portion of the spindle motor hub based upon the detected spindle motor imbalance location indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation. In another embodiment, the off-set may be minimized. For example, the method may include equally spacing the inner edge of the disk away from the spindle motor hub based upon the detected spindle motor imbalance location indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation.
According to another aspect of the present invention, there is provided a disk drive including a disk drive base and a disk pack rotatably coupled to the disk drive base. The disk pack includes a rotatable disk and a spindle motor configured to rotate the disk about an axis of rotation of the spindle motor. The spindle motor has a spindle motor imbalance location indicia upon the spindle motor indicative of a location of a spindle motor location imbalance. The disk is attached to the spindle motor with the disk being off-set from the axis of rotation in relation to spindle motor imbalance location indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation.
According to various embodiments, the spindle motor may have a spindle motor imbalance magnitude indicia upon the spindle motor indicative of a magnitude of a spindle motor location imbalance. The disk may be attached to the spindle motor with the disk off-set from the axis of rotation based upon the detected spindle motor imbalance magnitude indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation. The disk drive may further include multiple disks upon the spindle motor. The disks may be attached to the spindle motor with the disks off-set from the axis of rotation in relation to the spindle motor imbalance location indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation. The disk drive may further include a disk clamp for attaching the disk to the disk clamp with the disk between the disk clamp and the spindle motor. The spindle motor may include a spindle motor hub and the disk includes an inner edge. A portion of the inner edge of the disk is disposed against a portion of the spindle motor hub based upon the spindle motor imbalance location indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation. In another embodiment, the inner edge of the disk may be equally spaced away from the spindle motor hub based upon the spindle motor imbalance location indicia for balancing the disk pack by producing a disk off-set imbalance in relation to the axis of rotation.